There was a shock when the prow of the Black Bear struck a canoe
which lay full in its path. The momentum was retarded for only a
second. Then the motor boat was beyond the line of war canoes with
their screaming, gesticulating occupants.

Looking out of the rear ventilator, Frank saw a smashed canoe
running down with the current, with a dozen or more natives clinging
to it. But there was still a large number of canoes up the river,
and the Black Bear was struck more than once by forceless bullets
and poisoned arrows as she sped past them.

Armed with modern rifles, the Indians would have made short work of
the occupants of the Black Bear, but the muskets they used were old
and mostly out of condition. The arrows were far more deadly,
although they stood less chance of penetrating the tough panels.

"Now," Harry said, as they passed a racing fleet of Indian boats,
"we can open up a little and get a breath of fresh air! I'm just
about suffocated!"

"Not just yet," Jack, who was at the front, said, "for there's a
mess of the black scamps just ahead. They are on the bank, both
banks, and seem to be waiting for something to happen. I wonder
what it can be?"

"Some trap, I suppose," Harry gritted. "Well, all we can do is to
ran on through them, if they come out in boats, and get out of their
reach. We ought to be able to be out of this blasted country in a
couple of hours."

"Because she doesn't know that this is the Black Bear. That is an
easy one! If she did she'd be here in a second."

The boys studied the lights a moment and then turned their attention
to the Indians, who were now making a great clamor. In a short time
it was easy to see what they were up to.

Above roared the falls and the rapids. At this point in the Beni
river there is a swift drop from the mountain plateau above. It
will be remembered that the Beni reaches away up into the Illimani
mountains, with its springs not far distant from the summit of the
Andes.

Where the boys were the Paredon and the Paderneira, falls and the
Araras and the Misericordia rapids made the navigation of the river,
even in the protected Black Bear, impossible for many miles. The
Indians seemed to understand this, for they had gathered at the foot
of the falls, possibly expecting to see the craft attempt the
ascent.

"And go to kingdom come with her?" laughed Jack. "Not any of that
for me. I'm headed, eventually, for little old N.Y."

"I'm tired of fooling with these cannibals," Frank explained. "We
haven't molested them, and yet they are after our scalps. They'll
get them, too, if something isn't done--and done right away, at
that."

"I'm with you!" Jack exclaimed. "I'm willing to try anything once.
Only let me in on the secret!" he added, chuckling.

"You had it right," Frank said. "What I propose is to blow the
Black Bear into smithereens, and about a thousand of those
bloodthirsty natives with it. The world will be all the better for
their being out of it. They are worse than the savage beasts in the
forests."

Harry looked mystified for a moment, and then said, speaking loudly
in order that his voice might be heard above the shouts of the
savages and the beating of arrows against the panels of the boat:

"It looks as if we'd have to do it. I hate to leave the Black Bear
in such a mess away off here in South America, but I don't see how
we are to get her out. The Wolf will carry us all right, I
suppose?" he said, tentatively.

"Sure thing!" Frank replied. "I've been thinking it all out. We'll
do it this way: When we get ready we'll put on full speed ahead on
the motors, with the prow turned against that obstruction below.
Then we'll hop into the Wolf and shut everything down tight. The
Black Bear will weaken the jam below, and the sharp nose of the Wolf
will poke through the rest of the logs and canoes. And there you
are!"

"Free of the natives, and bobbing down the, river in safety!" cried
Jack. "That looks good to me!"

"Well," Frank replied, "we've got to use the Black Bear for a
battering ram anyway, and she'll be all smashed up, so we may as
well go the whole hog with her. We'll put a lot of dynamite down
under the motors and fix a cap so it will blow up when the
concussion comes. By that time the natives will be swarming around
her, and they'll get what's coming to them."

"And where will we be when the explosion is rocking this half of the
world?" demanded Harry. "Up in the air?"

"We'll be a cuddled up in the Wolf, between the lockers, with plenty
of grub and ammunition, sailing down the river in a bullet-proof
vessel. This move will burst up our meeting with the Nelson, of
course, but there is no other way. They'll get us if we remain
here."

While this talk had been going on, the cannibals had drawn nearer to
the Black Bear, pressing forward from both banks in canoes and
pounding at the panels with their arrows. It seemed only a question
of time when they would board the craft and force the panels. Their
shouts of victory were shrill and exasperating.

"You see how it is," Frank said, "the Black Bear can never be pushed
up over the falls, and we can never get her past the obstructions
below, even by the use of dynamite. If we could blow the those logs
out of the way, the Indians would board us instantly. We could give
them only a charge or two of dynamite and a few shots before they
would be inside. Now' we can drift down the river in the Wolf
without fear of entertaining man-eaters on board. They may get on
top of the boat, but they can never get inside."

"And so we'll have to give up our trip!" wailed Harry. "We'll have
to drift down stream in that hot hole and take a steamer at the
nearest river town!"

"It strikes me," Frank observed, "that it is a mighty good thing
we've got that hot hole to drift down stream in. If the Black Bear
had only been constructed on the principle of the Wolf, we'd be in a
position to give these heathens the laugh. Well, let us pull the
Wolf up and throw out stuff enough to give us room. Then we'll get
out the dynamite."

The boys drew the Wolf up by the cable as Frank tried to elude the
watchful eyes of the savages long enough to open the hatch on top
and climb inside, but a dozen arrows whizzed by his head when he
looked out.

"Dynamite," almost shouted Jack. "We'll give them dynamite as long
as it lasts, and then ram the logs below."

"We may kill, a couple of hundred," Frank said, "but it seems to me
that there will be about ten thousand left."

The boys were indeed in a tight box. With their automatics and
their dynamite they might keep the natives at bay for a time, but in
the end they would be obliged to surrender or starve to death.

"Well," Jack said, grimly, "let's get out the dynamite. I want to
see some of these devils blown up!"

Just then an arrow struck the plate glass panel at the top of the
Black Bear's deck covering and Jack looked up. He gazed a moment in
wonder and then let out a shout that rose above the yelling of the
savages and the pounding of arrows against the panels of the Black
Bear.

The aeroplane was only a few yards above the Black Bear. Already
the natives were slinking away in their canoes. Those on the banks
were slowly withdrawing into the shelter of the forests.

"They're running away!" Jack cried. "Now we'll have some fun with
good old Ned Nestor!"

For a moment it looked as if the statement was correct; as if the
natives, alarmed at the sight of the aeroplane would disappear from
sight without a fight. But this supposition was soon disproved.

As the Nelson came nearer, a dozen bullets from the forests struck
her planes. The boys, in the boat raised the panel and shouted to
the aviator to look out for poisoned arrows.

Then the aeroplane shot up again. They could see that there was
only one person on the machine, and that he was busy arranging
something which looked like a stick of dynamite which he held in his
hands.

In a moment something grim and sinister whirled and hissed through
the air, and then there came a terrific explosion in the forest to
the right. Trees were leveled, and a great hole showed in the bank.
In an instant, following close on the roar of the dynamite, there
came a chorus of cries from savage throats-cries of fear, of terror,
of rage--and then silence.

For a moment it seemed as if the forests held no forms of animal
life, then the sharp call of the tiger-cat, the wail of the puma,
the chattering of the monkeys, came to the ears of the listening
boys.

"I guess this coming act will consist of a feed for the wild
beasts!" Jack said.

For a long time there was no sound of savage life in the forests,
save that from the throats of beasts of prey, scenting blood and
slowly drawing closer to the river's banks. The boys on the Black
Bear looked into each other's faces and wondered.

"I take it that they think there's something supernatural in this
dropping of dynamite from the sky," Harry observed. "Anyway, they
seem to have taken themselves off, and we'll open up and signal to
the Nelson! Say, won't it be fine to see good old Ned Nestor again?
I wonder how he knew we were here?"

"And I wonder where Jimmie and Leroy are?" Harry reflected. "There
is only one person on the machine, and that must be Ned."

Jack was about to throw open the top panels when he caught sight of
the aeroplane again, nearer to the water than before.

"We must be nearer the falls than we thought, for the water seems to
be a ripple about us. Rear it! I'm going to look out and see it
looks like."

In a moment he was jamming the panel shut and springing the slides
over the loopholes and the ventilators.

Jack sprang to the prow, not knowing what danger threatened, but
obeying the sudden gestures of his chum to close every opening.
Before he sprung the steel panel over the ventilator he glanced
out on the river.